wip:

.gitignore

@@ -0,0 +1,4 @@
+.pio
+.vscode
+.DS_Store
+platformio.ini

src/main.c

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+#include "avr/io.h"
+#include "stdio.h"
+
+#define BAUD_RATE 9600
+#define BAUD_PRESCALE (F_CPU / 16 / BAUD_RATE - 1)
+
+int usart(char byte, FILE *stream)
+{
+	while ((UCSR0A & (1 << UDRE0)) == 0)
+	{
+	}
+	UDR0 = byte;
+	return 0;
+}
+FILE uart = FDEV_SETUP_STREAM(usart, NULL, _FDEV_SETUP_WRITE);
+
+int main(void)
+{
+	UBRR0H = (BAUD_PRESCALE >> 8);
+	UBRR0L = BAUD_PRESCALE;
+	UCSR0B = (1 << RXEN0) | (1 << TXEN0);
+	UCSR0C = (1 << UCSZ01) | (1 << UCSZ00);
+	stdout = &uart;
+	return 0;
+}